We look into the engineering reasons why the Francis Scott Key bridge collapsed after a ship crashed into it. Also, a new analysis finds that more viruses spread from humans to animals than from animals to humans.The Engineering Behind Why The Bridge In Baltimore CollapsedOn Tuesday, a large section of Baltimore’s Francis Scott Key bridge collapsed after an enormous container ship lost power and collided with the structure. Two people were rescued from the water, two bodies were recovered, and four others are unaccounted for and presumed dead.The structural failure of the bridge, which cut off a key roadway and a major international shipping port, has many wondering why this happened. Does the fault lie in aging infrastructure or in the manner the container ship struck one of the bridge’s main supports?Guest host Arielle Duhaime-Ross talks to journalist Swapna Krishna about the engineering reasons behind why the bridge collapsed and other top stories in science this week, including rockets NASA is launching during next week’s solar eclipse, new research about how Homo sapiens traveled out of Africa, and visualizing the magnetic field of the black hole at the center of our galaxy.Mapping Out How Viruses Jump Between SpeciesIn the world of emerging infectious diseases, one of the looming threats comes from the so-called zoonotic diseases—pathogens that somehow make the jump from an animal host to a human one. This includes pathogens such as COVID-19 and avian influenza, a.k.a. bird flu, which can sometimes cross the species divide. But a new analysis published in the journal Nature Ecology and Evolution finds that when it comes to viruses, more viral species appear to have jumped from humans to animals than the other way around. And even more cases of interspecies transmission don’t involve humans at all.Cedric Tan, a PhD student in the University College London Genetics Institute and Francis Crick Institute, joins guest host Arielle Duhaime-Ross to talk about the analysis, and what it tells us about our place in a global web of viruses.Transcripts for each segment will be available after the show airs on sciencefriday.com.  Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.